The maternal effect homeotic gene fs(1)h of Drosophila has been studied by genetic and molecular techniques. The gene has been cloned previously. In the current year, the zygotic effect of fs(1)h mutations has been analyzed, indicating the fs(1)+ gene product is required through larval stages. Analysis of fs(1)h transcripts revealed a complex pattern: In the ovary major 7.6 and 5.9 kb RNAs occur, in larvae 5 different moleules are found including two species between 8 and 9 kb, and a single 2.4 kb transcript occurs in pupae. Cloned cDNAs corresponding to most sequences of the ovarian RNAs have been isolated. Analysis of these clones indicates the presence of at least 5 introns in the fs(1)h gene, and suggests that the 7.6 and 5.9 kb RNAs have a common 5' region but different 3' segments. These results, together with earlier genetic data, suggest that the proximal (5') region of the locus is involved in segment identity (i.e., responsible for homeotic effects), while the distal (3') region carries functions for embryo survival. The fs(1)h transcripts are uniformly distributed in the oocyte and embryo, as determined by in situ hybridization. A repetitive sequence, named pen, has been characterized in the D. melanogaster genome. Unlike most repeated elements in this animal, the pen sequence is not precisely defined in its length or sequence, but rather constitutes a sequence motif composed of clustered GGX triplets where X can be any nucleotide. This sequence could encode poly-glycine stretches that might form flexible protein domains.